Update subprocess2.check_output() to behave like subprocess.check_output().

PRESUBMIT.py

 # Copyright (c) 2011 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Top-level presubmit script for depot tools.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts for
 details on the presubmit API built into depot_tools.
 """
 
@@ skipping 67 matching lines @@
       if test in DISABLED_TESTS or not test.endswith('.sh'):
         continue
 
       print('Running %s' % test)
       try:
         if input_api.verbose:
           input_api.subprocess.check_call(
               [input_api.os_path.join(test_path, test)], cwd=test_path)
         else:
           input_api.subprocess.check_output(
-              [input_api.os_path.join(test_path, test)], cwd=test_path)
+              [input_api.os_path.join(test_path, test)], cwd=test_path,
+              stderr=input_api.subprocess.STDOUT)
       except (OSError, input_api.subprocess.CalledProcessError), e:
         results.append(output_api.PresubmitError('%s failed\n%s' % (test, e)))
   except local_rietveld.Failure, e:
     results.append(output_api.PresubmitError('\n'.join(str(i) for i in e.args)))
   finally:
     server.stop_server()
   return results
 
 
 def CheckChangeOnUpload(input_api, output_api):
   # Do not run integration tests on upload since they are way too slow.
   tests_to_black_list = [
       r'^checkout_test\.py$',
       r'^gclient_smoketest\.py$',
       r'^scm_unittest\.py$',
     ]
   return CommonChecks(input_api, output_api, tests_to_black_list)
 
 
 def CheckChangeOnCommit(input_api, output_api):
   output = []
   output.extend(CommonChecks(input_api, output_api, []))
   output.extend(input_api.canned_checks.CheckDoNotSubmit(
       input_api,
       output_api))
   output.extend(RunGitClTests(input_api, output_api))
   return output